Science in Society (SiS) is proud to feature the winners of the "Integrated Graduate Program in the Life Sciences (IGP) Science and Society Class Distinction Award." Written as part of a course on science and society, these papers were chosen to be published on SiS. This month, we present the following piece by graduate student Emma Flores.
The incidence of stroke is approximately twice as high for African Americans as compared to white Americans, and in the past ten years the incidence of diabetes has risen more in Hispanics than any other race in the United States.
These disconcerting statements are results from studies published in leading research journals describing the incidence of disease in different racial groups, exposing great health disparities among them. Uncovering the complex reasons for these disparities is a big priority for medical researchers. Contributing components include environmental factors, like living or working in areas with high levels of carcinogens present, and social factors, like differences in access to quality healthcare. Also important are genetic risk factors: a shared biology among a group of people that makes them more susceptible to a given disease.
However, the same advances in science and technology that are helping us better understand the biology of disease are also helping us better understand this shared biology between racial groups. And what researchers have learned might surprise you.
At the core of this issue is how we define “race.” The United States government recognizes five racial groups—White, Black or African American, Asian, American Indian or Alaskan Native, and Native Hawaiian or other Pacific Islander—and also distinguishes between “Hispanic” and “non-Hispanic.” These categories are used classify individuals in numerous professional fields, including healthcare. However, these classifications—including those made in the research studies mentioned above—are established using self-identified race, i.e., what the subject identifies his or her race to be. When individuals identify with a certain race, many factors often contribute, including one’s known ancestry, but also their culture. This self-identification is rooted more in the social perception of race than in biology.
The idea of race as a primarily social construct has been reinforced by what researchers have learned from the wealth of genetic studies conducted over the last few decades. From the development of DNA sequencing in the 1960’s to the more recent completion of the Human Genome Project, modern science has made great strides in understanding the genetic components underlying race. We now know that the human genome—our complete set of genetic information—contains three billion base pairs: a collection of A, C, T and Gs that match up with one another to produce a code. Specific regions of this code are responsible for biological traits and are called genes.
After scanning multiple genomes, we know that human beings only differ from one another in one out of every 1000 base pairs, meaning that we are 99.9% identical, regardless of race. With such a tremendous amount of identical DNA within the human genome, focusing on base pair differences called polymorphisms is a powerful way to examine how our genes contribute to differences among us. If similar polymorphisms are present within certain genes in a given race, then we can link these similarities to genetic differences between races. However, when scientists study polymorphisms in various genes (including genes that contribute to our most striking differences, including skin, hair, and eye color) they find greater variability within a race than between races. These results suggest that there is not a biological component to what we perceive as race.
Despite not having genetic indicators for race, scientists have recently identified genetic markers for ancestry. Ancestry, in contrast to race, is based solely on genetic lineage, rather than other factors like cultural identification. By once again using DNA sequencing to screen polymorphisms, researchers have found select polymorphisms that occur with a high frequency in human populations from different geographical regions of the world. These polymorphisms are not located in genes that are responsible for outward appearances. Instead, they are used to estimate the geographical ancestry of an individual, and for this reason they are referred to as ancestry informative markers (AIMs). The collections of AIMs used today determine the proportion of an individual’s ancestry that stems from the four main indigenous populations: European, African, East Asian, and Native American. An example of an AIM used by scientists in the United States is called Duffy Null. This polymorphism is located in a gene that produces red blood cells and is found within individuals from West African ancestry.
So what does this mean for biomedical studies based on self-identified race, rather than genetic ancestry? In a 2006 study published in the New England Journal of Medicine, scientists examined genetic ancestry using AIMs in a sample population of self-reported white individuals and black individuals in Cleveland, Ohio. The study was established to explore if genetic variability regarding ancestry was present within self-identified races. What they found was very interesting.
Within the group of individuals that self identified as white, 93% were of predominantly European ancestry and 7% were of mixed-race ancestry. Within the group that self identified as black, only 4% of individuals were of predominantly African ancestry, 94% were of mixed race ancestry, and 2% were of predominantly European ancestry. When similar analysis from a different study was done in groups of self-identified Hispanics in the United States, scientists found that Hispanics living in the West and Southwest contain mostly European and Native American ancestry with little African ancestry, while Hispanics living along the East Coast and in Florida contain European and African ancestry with little Native American ancestry. Taken together, these results show a substantial amount of genetic variability regarding ancestry within self-identified races in the United States.
Given the tremendous variability within racial groups, using such an imprecise classification in medical research studies could actually mask the true genetic components of complex diseases affecting certain populations. However, the discovery of AIMs has provided science with a powerful tool to genetically determine ancestry and combat this issue. It would be incorrect to regard AIMs as genetic identifiers of race; rather, they represent a more accurate and effective classification for conducting biomedical research. How this tool will ultimately be used—and how it might change the way we view ourselves—remains to be seen.